Améliorer la qualité du code source à l’aide de la complexité cognitive

Depuis 40 ans, la Compléxité Cyclomatique est defacto le standard pour mesurer le niveau de testabilité et maintenabilité du code source. Mais cette métrique souffre de beaucoup de limitations avec les languages modernes. Pour cette raison, SonarSource a publié une nouvelle métrique en 2016 beaucoup plus représentative du niveau de maintainabilité du code source: la Complexité Cognitive.

Cette session d'introduction permet de comprendre cette nouvelle métrique au travers de nombreux exemples de code open source issues notamment de SonarCloud.io.

Vous verrez également comment produire un code de meilleur qualité et retravailler du code existant en s'appuyant sur la Complexité Cognitive.

Transcript

1. #DevoxxFR Améliorer la qualité du code source à l’aide de la complexité cognitive Xavier Bourguignon @xbourguignon 1
2. #DevoxxFR 2 Complexité cognitive ?
3. #DevoxxFR 3
4. #DevoxxFR 4 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; }
5. #DevoxxFR 5 Complexité cyclomatique ?
6. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; } 6
7. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; } 7
8. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; } 8
9. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +1 if (i % j == 0) { continue OUT; } } total += i; } return total; } 9
10. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +1 if (i % j == 0) { // +1 continue OUT; } } total += i; } return total; } 10
11. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +1 if (i % j == 0) { // +1 continue OUT; } } total += i; } return total; } // cyclomatic complexity 4 11
12. #DevoxxFR Exemple 2 String getWords(int number) { switch (number) { case 1: return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } 12
13. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } 13
14. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: // +1 return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } 14
15. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: // +1 return "one"; case 2: // +1 return "a couple"; case 3: return "a few"; default: return "lots"; } } 15
16. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: // +1 return "one"; case 2: // +1 return "a couple"; case 3: // +1 return "a few"; default: return "lots"; } } 16
17. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: // +1 return "one"; case 2: // +1 return "a couple"; case 3: // +1 return "a few"; default: return "lots"; } } // cyclomatic complexity 4 17
18. #DevoxxFR 18
19. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { // +1 int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +1 if (i % j == 0) { // +1 continue OUT; } } total += i; } return total; } // cyclomatic complexity 4 19
20. #DevoxxFR Exemple 2 String getWords(int number) { // +1 switch (number) { case 1: // +1 return "one"; case 2: // +1 return "a couple"; case 3: // +1 return "a few"; default: return "lots"; } } // cyclomatic complexity 4 20
21. #DevoxxFR 21 Complexité cognitive
22. #DevoxxFR 22
23. #DevoxxFR 23 Ignorer les structures lisibles
24. #DevoxxFR 24 Casse le flux
25. #DevoxxFR 25 Imbrication
26. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; } 26
27. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { if (i % j == 0) { continue OUT; } } total += i; } return total; } 27
28. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +2 if (i % j == 0) { continue OUT; } } total += i; } return total; } 28
29. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +2 if (i % j == 0) { // +3 continue OUT; } } total += i; } return total; } 29
30. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +2 if (i % j == 0) { // +3 continue OUT; // +1 } } total += i; } return total; } 30
31. #DevoxxFR Exemple 1 int sumOfPrimes(int max) { int total = 0; OUT: for (int i = 1; i <= max; ++i) { // +1 for (int j = 2; j < i; ++j) { // +2 if (i % j == 0) { // +3 continue OUT; // +1 } } total += i; } return total; } // cognitive complexity 7 31
32. #DevoxxFR Exemple 2 String getWords(int number) { switch (number) { case 1: return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } 32
33. #DevoxxFR Exemple 2 String getWords(int number) { switch (number) { // +1 case 1: return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } 33
34. #DevoxxFR Exemple 2 String getWords(int number) { switch (number) { // +1 case 1: return "one"; case 2: return "a couple"; case 3: return "a few"; default: return "lots"; } } // cognitive complexity 1 34
35. #DevoxxFR 35 En vrai ça donne quoi ?
36. #DevoxxFR 36 Refactoring patterns
37. #DevoxxFR if (condition) { ... } else { if (une_autre_condition) { ... } else { if (une_3ème_condition) { ... } } } 37
38. #DevoxxFR if (condition) { ... } else { if (une_autre_condition) { ... } else { if (une_3ème_condition) { ... } } } 38
39. #DevoxxFR Collapse ! if (condition) { ... } else if (une_autre_condition) { ... } else if (une_3ème_condition) { ... } 39
40. #DevoxxFR Collapse ! if (condition) { ... } else if (une_autre_condition) { ... } else if (une_3ème_condition) { … } 40
41. #DevoxxFR if (condition) { ... return_value = ‘toto’ } else if (une_autre_condition) { ... return_value = ‘titi’ } else if (une_3ème_condition) { ... return_value = ‘tutu’ } return return_value 41
42. #DevoxxFR if (condition) { ... return_value = ‘toto’ } else if (une_autre_condition) { ... return_value = ‘titi’ } else if (une_3ème_condition) { ... return_value = ‘tutu’ } return return_value 42
43. #DevoxxFR Early return !! if (condition) { ... return ‘toto’ } if (une_autre_condition) { ... return ‘titi’ if (une_3ème_condition) { ... return ‘tutu’ } 43
44. #DevoxxFR Early return !! if (condition) { ... return ‘toto’ } if (une_autre_condition) { ... return ‘titi’ if (une_3ème_condition) { ... return ‘tutu’ } 44
45. #DevoxxFR if (my_value == 1) { ... } else if (my_value == 2) { ... } else if (my_value == 3) { ... } else if (my_value == 4) { … } 45
46. #DevoxxFR if (my_value == 1) { ... } else if (my_value == 2) { ... } else if (my_value == 3) { ... } else if (my_value == 4) { … } 46
47. #DevoxxFR Switch !!! switch (my_value) { case 1: ... case 2: ... case 3: ... case 4: ... } 47
48. #DevoxxFR Switch !!! switch (my_value) { case 1: ... case 2: ... case 3: ... case 4: ... } 48
49. #DevoxxFR try { ... } catch (NullPointerException ex) { logger.log(ex); throw ex; } catch (IOException ex) { logger.log(ex); throw ex; } catch (SQLException ex) { logger.log(ex); throw ex; } 49
50. #DevoxxFR try { ... } catch (NullPointerException ex) { logger.log(ex); throw ex; } catch (IOException ex) { logger.log(ex); throw ex; } catch (SQLException ex) { logger.log(ex); throw ex; } 50
51. #DevoxxFR Multi catch !!!! try { ... } catch (NullPointerException|IOException| SQLException ex) { logger.log(ex); throw ex; } 51
52. #DevoxxFR Multi catch !!!! try { ... } catch (NullPointerException|IOException| SQLException ex) { logger.log(ex); throw ex; } 52
53. #DevoxxFR try { conn = ds.getConnection(); s = conn.createStatement(); rs = s.executeQuery(requete); ... } catch (SQLException e) { e.printStackTrace(); } finally { if (rs != null) { try { rs.close();} catch (SQLException e) { } rs = null; } if (s != null) { try { s.close(); } catch (SQLException e) { } s = null; } if (conn != null) { try { conn.close(); } catch (SQLException e) { } conn = null; } } 53
54. #DevoxxFR try { conn = ds.getConnection(); s = conn.createStatement(); rs = s.executeQuery(requete); ... } catch (SQLException e) { e.printStackTrace(); } finally { if (rs != null) { try { rs.close();} catch (SQLException e) { } rs = null; } if (s != null) { try { s.close(); } catch (SQLException e) { } s = null; } if (conn != null) { try { conn.close(); } catch (SQLException e) { } conn = null; } } 54
55. #DevoxxFR Helpers !!!!! try { conn = ds.getConnection(); s = conn.createStatement(); rs = s.executeQuery(requete); ... } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(s); DbUtils.closeQuietly(rs); DbUtils.closeQuietly(conn); } 55
56. #DevoxxFR Helpers !!!!! try { conn = ds.getConnection(); s = conn.createStatement(); rs = s.executeQuery(requete); ... } catch (SQLException e) { e.printStackTrace(); } finally { DbUtils.closeQuietly(s); DbUtils.closeQuietly(rs); DbUtils.closeQuietly(conn); } 56
57. #DevoxxFR 57
58. #DevoxxFR 58
59. #DevoxxFR https://www.sonarsource.com/docs/CognitiveComplexity.pdf 59
60. #DevoxxFR Merci 60
61. #DevoxxFR Questions ? 61